This application is based on application No. 11-184586 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a distance measuring apparatus for measuring as distance information the round-trip propagation time of light to an object that reflects light.
2. Description of the Related Art
By measuring the so-called time of flight (TOF) from transmission of light pulse to reception of the pulse returning after reflected at an object, the distance to the object can be obtained through application of the known light propagation velocity. This method is applied in various fields such as civil engineering and astronomy. In principle, the closer to zero the pulse width is, the higher the measurement accuracy is. In actuality, however, the pulse width is larger than a value depending on constraints such as the response of the light source and the reception sensitivity. In general distance measuring apparatuses, the pulse width is approximately 50 to 100 ns where resolution of approximately several centimeters is obtained, and the waveform is unimodal. By determining the reception point of time by detecting the peak of the received light waveform, measurement can be performed with a high degree of accuracy irrespective of the amplitude of the received light waveform.
Conventionally, there has been a high possibility that a measurement value being low in reliability because the amplitude or the waveform of the received light pulse is incorrect due to low reflectance of the object or incidence of extraneous light is used as a correct measurement value. Moreover, there are occasions when the user ends measurement without noticing that since the object is too far or too dose, measurement is impossible and no measurement value is obtained.
An object of the present invention is to enable the user to check whether the measurement result is collect or not.
Another object of the present invention is to improve practicality by increasing the permissible range of a measurement condition.
According to the present invention, a distance measuring apparatus outputting measurement data responsive to a time from a transmission point of time to a reception point of time of pulse light, comprises: a projector that projects pulse light outside; a light receiver that receives the pulse light reflected in the outside; determining means for determining whether a received light waveform of the received light is correct waveform or incorrect waveforms including at least two incorrect waveforms, based on an output signal of the light receiver; and warning data outputting means for outputting warning data responsive to a result of the determination when the determining means determines that the received light waveform is incorrect.
Moreover, the distance measuring apparatus performs measurement again when the determining means determines that the received light waveform is incorrect.
Moreover, the distance measuring apparatus further comprises a controller that changes an operation setting of at least one of the projector and the light receiver based on a latest result of the determination by the determining means before measurement is performed again.
Moreover, the warning data outputting means outputs the warning data when it is determined that the received light waveform is incorrect in a last time re-measurement of a set number of re-measurements.
Moreover, according to the present invention, a distance measuring apparatus outputting measurement data responsive to a time from a transmission point of time to a reception point of time of pulse light, comprises: a projector that projects pulse light outside; a light receiver that receives the pulse light reflected in the outside; a storage medium for storing an output waveform of the light receiver therein; determining means for determining whether the output waveform stored in the storage medium is correct or incorrect; and warning data outputting means for outputting warning data responsive to a result of the determination when the determining means determines that the output waveform is incorrect.